IWAD

The acronym IWAD is generally interpreted as "internal WAD" and refers to a WAD file which contains all of the external data for a complete game. In order to be identified as an IWAD, a file must contain the "IWAD" magic identifier as the first four bytes in its header. An IWAD file is required for execution of any of the stock Doom engine games. This is in contrast to PWADs, which are "patch" WADs intended to replace or augment the content found in the IWAD.

Resources
A complete IWAD file usually contains the following, along with other types of resources:


 * Levels for each level in the game
 * PLAYPAL, COLORMAP and ENDOOM lumps
 * TEXTURE and PNAMES lumps for the game's texture information
 * A complete set of sounds
 * A complete set of music lumps
 * Graphics for the menu, status bar, heads-up display, font, intermission and finale screens
 * A complete set of sprites
 * A complete set of patches (matching those found in PNAMES)
 * A complete set of floor textures (flats)

When the game's executable file is started, one of the first things it does is attempt to locate an IWAD file. This is done based on file name; the executable has the names of the Doom, Heretic, Hexen, or Strife IWAD files stored in an internal list.

The executable sets an internal "mode" dependent on the IWAD it finds; because of this, what constitutes "a complete set" in the above lists depends on the name of the IWAD. For example, different music lumps will be used depending on whether the executable is configured to play Doom or Doom II. The executable also behaves differently in other ways: for example, loading of PWADs is disabled when loading a shareware IWAD.

Because of this, it is possible to use the executable from one Doom game with the IWAD file of another, although there are some exceptions to this due to version issues. For example, the Doom II executable cannot be used with a Final Doom IWAD, as that executable was created before Final Doom was released. (The Final Doom IWAD, however, could be renamed to doom2.wad, or loaded as a PWAD.)

Unlike many PWADs, IWADs are not meant to ever be loaded together when starting a game, even in source ports. There exist certain workarounds, such as WadSmoosh, a tool able to merge multiple IWADs into one to allow all content to be played on a single unified IWAD.

Official
The following table lists the canonical file names of officially licensed games' IWAD files.

Unofficial
Since the release of the Doom source code and development of advanced source ports, the creation of custom IWAD files which implement new games has become viable.